The invention relates generally to multi-wheel drive vehicles and, more particularly, to the steering of multi-wheel drive vehicles such as, for example, wheelchairs and the like.
Generally, a multi-wheel drive vehicle is any vehicle that has more than one wheel that is used to power or drive the vehicle. Examples of such vehicles include two and four wheel drive wheelchairs. Driving such vehicles in straight lines does not pose significant control issues. However, this is generally not the case when driving such vehicles into turns. More specifically, to drive a multi-wheel drive vehicle into a turn requires that each of the wheel drives have differing velocities in order to achieve the turn.
If these differing velocities are not properly realized in the wheel drives, several undesirable consequences result. For example, if one or more of the wheel drives has a velocity below that required to make the turn at a particular vehicle speed, those affected wheel drives will at least partially xe2x80x9cdragxe2x80x9d along the riding surface. This is undesirable for several reasons. First, it creates wear on the wheel component of the wheel drive. Second, it creates wear on the riding surface. If the riding surface is, for example, a carpet, then such carpet may be damaged by such dragging action. If one or more of the wheel drives has a velocity above that required to make the turn, the vehicle will not effectively make the desired turn because the vehicle suffers from understeer. Additionally, such non-optimal control of the wheel drives leads to higher energy consumption by the vehicle, which significantly reduces the vehicle""s range. Hence, it is desirable to provide a system and method for controlling a multi-wheel drive vehicle that does not suffer these drawbacks.
According to one embodiment of the present invention, a method of controlling a multi-wheel drive vehicle is provided. The method is preferably applicable to the steering of such a vehicle and determines the individual velocities for each wheel drive. In this regard, the method includes two general steps. The first step includes determining the distance of each wheel drive and a vehicle velocity reference point from a turning reference point. The second step includes ratioing two components: the distance from the turning reference point to each wheel drive and the distance from the turning reference point to the vehicle velocity reference point. The ratios are then applied to a vehicle velocity that is associated with the vehicle velocity reference point, to determine the velocity of each respective wheel drive. Once determined, the velocities are output to each wheel drive.
According to another embodiment of the present invention, a method of controlling a multi-wheel drive vehicle includes, for example, the step of determining a turning reference, vehicle velocity, and reference distance. The reference distance is the distance between the turning reference and a known reference position relative to the vehicle. The method further includes, for example, determining a wheel drive distance and velocity for each wheel drive. The wheel drive distance is the distance of each wheel drive from the turning reference. The velocity for a wheel drive is determined from the wheel drive distance, reference distance and vehicle velocity. Once the velocity for each wheel drive has been determined, it is outputted to each wheel drive.
According to another embodiment of the present invention a system for controlling a multi-wheel drive vehicle is provided. The system includes, for example, an input device, a controller in circuit communication with the input device, at least two wheel drives in circuit communication with the controller, and logic for determining the individual velocities for the at least two wheel drives.
Hence, the present invention is particularly useful for any vehicle having two or more wheel drives. The present invention is also applicable to any vehicle that allows for individual wheel drive control. Such vehicles include electrically driven vehicles and combustion engine driven vehicles. The present invention is also particularly useful in that it can replace conventional transmissions including differential gearboxes, four wheel coupling transmissions, and special xe2x80x9cviscoxe2x80x9d clutches, just to name a few. It should also be noted that the present invention can also be used with such conventional transmissions that allow for individual wheel drive control.
Therefore, it is an advantage of the present invention to provide a method of steering a multi-wheel drive vehicle by determining the velocity of each individual wheel drive.
It is another advantage of the present invention to provide a system for steering a multi-wheel drive vehicle that includes a means for determining the individual velocities of each wheel drive.
It is yet another advantage of the present invention to provide a surface tolerant drive system that includes a means for driving a vehicle when the wheel drives are on differing surfaces.